In general, substances expand by heat. Organic resin materials are particularly known to have high linear expansion coefficients. For example, in use of members composed of organic resin materials for devices such as precision optical systems, a member having a high linear expansion coefficient and exhibiting a large change in size by temperature changing may cause displacement in an optical system.
As a measure for solving this problem, there is known a method for compensating the change in size by incorporating a material having a negative linear expansion (hereinafter, referred to as “negative expansion”) property into the periphery of a member composed of an organic resin material. Examples of the material having a negative expansion property include inorganic materials such as zirconium tungstate (PTL 1), lithium-aluminum-silicon oxides, and nitrides of manganese. In addition, organic materials such as liquid crystal polymers and ultrahigh molecular weight polyethylene fibers are known as materials showing negative expansion properties (PTL 2).
However, the use of an inorganic material having a negative expansion property for compensating the thermal expansion of an organic resin material has disadvantages such that molding at a temperature of 400 degrees (Celsius) or less is difficult and that it causes an increase in weight. In addition, the organic material having a negative expansion property mainly exhibit the negative expansion property in a fiber or sheet state, and it is difficult to exhibit the property in a bulk state.
Furthermore, in materials that are known to have negative expansion properties, the absolute value of the linear expansion coefficient is about 25*10−6/degree (Celsius) at a maximum. Accordingly, in order to compensate the expansion due to a change in the temperature of an organic resin material, a molded article of such a material having a negative expansion property must have a considerably large thickness or amount.